Is it possible to determine the instantaneous radial velocity of a star by observation? instantaneous tangential velocity?

The radial velocity is determined from the line spectrum based on the longitudinal Doppler effect. Instantaneousness is limited by the exposure time of the spectrogram.
To determine the average tangential velocity component, positional observations separated by a large time interval (several years or more) are required. Determination of instantaneous tangential velocity is not possible.

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